The present invention relates to a thread-cutting chuck which operates with minimum amounts of lubrication having an axially central lubricant channel for connecting an insert sleeve for the collet chuck, particularly a quick-change insert, which accommodates a screw tap that is provided with a longitudinal borehole, with a minimum lubrication source on a machine side, from which the lubricant is passed as an aerosol to the longitudinal borehole of the screw tap, and wherein the lubricant channel, in the junction region leading into the insert sleeve, comprises an axially displaceable coolant pipe which brings about a direct connection with the longitudinal borehole of the screw tap.
Known thread-cutting chucks in which an aerosol of the cooling lubricant, which is dispersed finely in the compressed air, serves to cool the thread-cutting site, as well as to lubricate the thread-cutting tap in the threaded borehole that is to be cut, are presently on the market in various embodiments. With such a thread-cutting chuck, the difficulty exists that screw taps of different sizes must be used, which protrude inwardly in each case to a different extent. This results in chambers of undefined size behind the screw tap. In these chambers, the danger exists that, due to turbulence, the aerosol will demix from the transporting compressed air. The droplets of cooling lubricant, which are required to be very finely dispersed, can ball together into large drops, in which case the cooling and lubricating effects are no longer provided to the degree desired.
German patent DE 42 18 237 A1 discloses a thread-cutting chuck of the type described above, in which, by providing a coolant pipe, a direct connection to the longitudinal borehole of the screw tap is possible without having to form a chamber between the pipe end and the screw tap. The sealing connection is accomplished in the disclosed thread-cutting chuck by way of a displaceable connecting piece which is at the end of the coolant pipe and can lie elastically against the screw tap. This known arrangement is, however, not suitable for aerosol lubrication since the coolant pipe protrudes at the inner end into a chamber, in which demixing of the aerosol would inevitably take place. In addition, such demixing would likely also occur at the connecting piece because of the differently expanding diameters present. Moreover, this type of sealing arrangement for the coolant at the end of the screw tap is suitable only for a particular axial position of the screw tap and not for a thread-cutting chuck with quick-change exchangeable inserts, for which the end surface of the screw tap is positioned axially at very different positions for drills of different thicknesses. The slight contact pressure springiness in the case of the aforementioned thread-cutting chuck disclosed in DE 42 18 237 A1 is neither intended for nor suitable for such axial positional displacements of the end of the screw tap.